Year	Percent
1960	4.67344
1961	5.59593
1962	6.94079
1963	6.98216
1964	7.0491
1965	7.15921
1966	7.27956
1967	7.3522
1968	7.25004
1969	6.95409
1970	6.52842
1971	6.07103
1972	5.72034
1973	5.56406
1974	7.19351
1975	10.51905
1976	10.77563
1977	10.93027
1978	11.0153
1979	10.96688
1980	10.84032
1981	8.92537
1982	5.2618
1983	5.22572
1984	5.22091
1985	5.20679
1986	5.20317
1987	5.17983
1988	5.13179
1989	5.03218
1990	4.92663
1991	4.589
1992	3.99595
1993	3.91187
1994	3.87583
1995	3.84658
1996	3.8317
1997	3.79007
1998	3.7516
1999	3.69004
2000	3.61663
2001	4.02377
2002	4.54447
2003	4.43712
2004	4.2909
2005	4.11826
2006	3.948
2007	3.79397
2008	3.68218
2009	3.62782
2010	3.62288
2011	3.62586
2012	3.60224
2013	3.55254
2014	3.48922
2015	3.39903
2016	3.31398
2017	3.2339